Male gorilla social ranking determines nurturing relationship with troop infants

A male gorilla's rank within its troop, and not its paternity, determines the bond that it will have with the band's infants, new research has shown.

The results of the study, which was carried out by the University of California with Lincoln Park Zoo, Chicago, supports the theory that throughout most of their evolution gorillas maintained a troop with just one adult alpha male.

However, they have now appended the theory with observations of modern gorillas, which allow several males in their band, with one acting as the father figure to all – i.e. the alpha male.

The aim of the study, led by Dr Stacy Rosenbaum of Lincoln Park Zoo and published in Animal Behaviour, was to determine the relationship that male mountain gorillas in Rwanda have with infants, and to discover how their behaviour compares to other primates which also have multiple males in the group.

They wanted to see if for troops with more than one male, the fathers could identify their children and vice versa. After analysing some 1,500 hours of data, they concluded that the paternal link that a male gorilla has to its children has no bearing on its relationship, but rather the higher the rank that adult males have in the group, the better and more nurturing bond they have with the infants.

It supports the theory that this is a relatively recent development in the social structure of gorillas, whose ancestors would have had one man per clan.

Rosenbaum said: "For a long time there was an assumption that monkeys and apes didn't know who their fathers were in groups with multiple males. Thanks to advances in molecular genetics, we now know that's not always true. We wanted to look at how male gorillas interact with infants to see if their behaviour supports this.

"When we think of a human alpha male, we have a very specific set of cultural norms that go along with that, like aggression and not being very paternal. In gorillas that's not the case at all; dominant males are often the biggest in the group, but they are gentle and nurturing with the infants."